A STUDY OF SURFACE INTERACTIONS OF GAMMA-ALUMINA, SILICA-ALUMINA, AND SILICA-MAGNESIA USING EPR SPECTRA OF ADSORBED NITRIC OXIDE

The EPR spectrum of the adsorbed NO molecule was used to determine crystal and magnetic field interactions on the surface of γ-alumina, silica-alumina, and silica-magnesia. The crystal-field splitting, Δ, of the 2pπ* levels of NO was found to be 0.75 eV on dehydrated γ-alumina and 0.60 eV on dehydrated silica-alumina. The spectrum on silica-magnesia indicated two adsorption sites with Δ equal to 0.60 and 0.33 eV. Spectra of NO on γ-alumina and silica-alumina show considerable hyperfine coupling with an 27Al atom at the adsorption site. The spectra were very similar to the spectrum of NO on a decationated Y zeolite. The maximum number of adsorption sites (as indicated by the spin concentration) was found to be 4(± 1) × 1012 sites/cm2 for 7-alumina and two types of silica-alumina. Silica-magnesia had 1.1(± 0.3) × 1012 sites/cm2. The number of sites and the shape of the spectra were a function of the degree of dehydration. Water added back to dehydrated γ-alumina and silica-alumina also affected the spectra. It appears that these adsorption sites are the α sites which Peri has studied using the IR spectra of adsorbed CO2. © 1969.